Drilling The Cretaceous/Paleogene Boundary in NJ: Testing the Relationship of Geochemical Anomalies to Event Beds

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The most recent mass extinction event that marks the Cretaceous/Paleogene (K/P) boundary occurred at 65 million years ago, resulted in the extinction of 90% of marine plankton and the dinosaurs. This extinction has been linked to the impact of a large asteroid (the Alvarez hypothesis) that has been traced to the Yucatan peninsula (Chicxulub, Mexico). However, recent studies in Texas and New Jersey have questioned the paradigm that the Chicxulub impact was the killer at the end of the Cretaceous. The Chicxulub impact spherules are reported below the boundary at Brazos, TX and an Ir anomaly occurs at the base of a layer of remarkable preservation of Cretaceous ammonites and mollusk fossils in New Jersey outcrops (the Pinna bed). In contrast, previous studies of Continental Dynamics/Ocean Drilling Program Leg 174AX onshore New Jersey coreholes and DSDP/ODP deep-sea coreholes suggest that there is one spherule layer associated with the extinction of the marine plankton overlain by a clay clast layer interpreted as a tsunamite. Outcrop and subsurface drilling has shown that the New Jersey coastal plain is an excellent location to recover complete and well-preserved K/P boundary sections. PIs will drill three closely spaced drilling transects of shallow (50-70 ft) holes on top of outcrops in New Jersey (Manasquan River, Fort Monmouth, and Crosswicks Creek) that will provide well-preserved material that is superior to outcrop sections for paleontological and geochemical analyses. They will also analyze in detail the Antioch Church, AL and Brazos, TX coreholes. Their working hypotheses are that there was one impact associated with one Ir anomaly and one spherule layer that was directly linked to the mass extinction event and that the extinction event was not causally related to major climatic or sea-level changes on the 100 kyr to million-year scale. Their hypotheses predict finding only one in situ spherule layer and one Ir anomaly in the sections to be intensely sampled.